The practical use of herbicides in crops is dependent on the presence of good selectivity in phytotoxicity between the crop being treated and the undesirable vegetation to be controlled. This selectivity is mainly a function of the inate phytotoxic properties of the herbicide employed. Methods of improving the selective action of herbicides so that they can be safely used in crop situations where selectivity is marginal are highly desirable. Such methods would expand the utility of the herbicide and any yield loss due to the herbicide's action on the crop treated would be ameliorated.
Crop selectivity has previously been improved for certain herbicides by a variety of means, such as by the co-application of non-herbicidal chemical safeners specific to the herbicide and the crop, the selective placement of the herbicide, the timing of the herbicide application, the use of certain inert formulation ingredients with the herbicide, and the physical form of the formulation employed. Generally, however, these methods, while helpful, do not completely solve the problem in most situations and are not at all effective in others. New methods of improving the crop selectivity of herbicides are needed.
Many of the recently discovered herbicides that are especially effective on grassy weeds, including the aryloxyphenoxypropanoates, such as diclofop, haloxyfop, quizalofop, fluazifop, fenoxaprop, and fenthiaprop, and the cyclohexanediones, such as sethoxydim and tralkoxydim, are generally only marginally selective for use in many grassy crops, such as wheat, barley, rice, corn, and sorghum. These classes of herbicides are known to inhibit the enzyme acetyl-coenyzme A carboxylase (ACCase) in susceptible plants (Plant Physiology, 85, 10-12, 1988).